Method of preparing cellulose acylate sulfates using sodium phosphate



3,075,964 Patented Jan. 29, 1963 3,075,964 METHOD OF PREPARING CELLULQSEACYLATE SULFATES USlNG SQDEUM PHQSPHATE Carl J. Malrn and Martin E.Rowley, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester,N .Y., a corporation of New Jersey N Drawing. Filed Mar. 27, 1961, Ser.No. 98,239 13 Claims. (Cl. 260-215) This application is acontinuation-inpart of US. patent application Serial No. 56,346, filedSeptember 16, 1960.

This invention relates to a method of preparing sodium cellulose acylatesulfates in which cellulose is esterified with a sulfating mixture oflower fatty acid anhydride, an alkali metal salt of acyl sulfuric acidand a weak noncombining acid esterification catalyst.

Various methods have been described in the prior art for preparingcellulose acylate sulfates such as U.S. Patents No. 1,866,532 of Haskinsand 2,582,009 and 2,622,079 of Crane. The procedure described by Haskinsinvolved the use of an esterifying bath of a pyridine salt of sulfuricacid in an excess of amine and lower fatty acid anhydride. The quantityof acyl introduced depended on the excess of anhydride employed. Thefirst patent to Crane relates to the preparation of acylate sulfates inacid form followed by neutralization after completion of the reaction.The Haskins method is expensive due to the high cost of organic amines.The first Crane method is critical in operation because of a highconcentration of strong mineral acid and, therefore, it is desirable inthat procedure to use a lower temperature to minimize degradation,although with good are obtained.

The second patent issued to Crane describes the use of an inorganic saltof sulfuric acid together with a slight excess of free sulfuric acid tocatalyze the acetylation portion of the reaction. This procedure resultsin the presence of neutral sodium sulfate in the mass, the presence ofwhich it is desirable to avoid.

One object of our invention is to provide a procedure for thepreparation of cellulose acylate sulfates which avoids the formation ofsodium sulfate in the esterification procedure. Another object of ourinvention is to provide a method of making celulose acylate sulfatesusing a Weak acid catalyst to promote the acylation and sulfation whichminimizes the danger of chain degradation of the cellulose. Anotherobject of our invention is to provide a process of making celluloseacylate sulfates in which cellulose is esterified with a lower fattyacid anhydride, a salt of acyl sulfuric acid and a weak acidesterification catalyst. A further object of our invention is to employalkali metal phosphate to provide both phos phoric acid catalyst andalkali metal ion to neutralize the acyl sulfuric acid in preparing anesterification bath for cellulose. Other objects of our invention willappear herein.

In its broader aspects, our invention comprises reacting upon celluloseor a hydroxyl-containing cellulose material such as partially hydrolyzedcellulose acetate with a lower fatty acid anhydride such as acetic,propionic or butyric anhydride in an esterification bath containing analkali metal salt of acyl sulfuric acid as the sulfating agent and anacid catalyst which is weaker than the first hydrogen and stronger thanthe second hydrogen of sulfuric acid in acetic acid. Acids which aretypical of catalysts of this nature are methane sulfonic acid,phosphoric acid and sulfoacetic acid. The proportion of acid catalystfor use may be selected by the individual operator from a Wide range.Quantities of weak acid catalyst as low as 0.05 mole per 100 parts ofcellulose will promote the esterifi cation while on the other hand,amounts of acid up to 3 or 4 times the amount of the cellulose may beused.

operation, good products In one embodiment of the invention, we reactalkali metal phosphate and acyl sulfuric acid, and react the resultingmixture, together with lower fatty acid anhydride, with hydroxylcontaining cellulose material.

In another embodiment of the invention, we react lower fatty acidanhydride, sodium phosphate and sulfuric acid, and react the resultingmixture, together with lower fatty acid anhydride, with a cellulosecompound containing free and esterifiable hydroxyl groups.

The esterification is carried out at a temperature within the range of100 F. No neutral sodium sulfate is formed and substantialesterification of the cellulose is obtained. Ordinarily it is desirableto employ cellulose as the starting material but if desired, one mayemploy a cellulose ether or a partially hydrolyzed cellulose acetate orcellulose propionate such as a cellulose acetate which has beenhydrolyzed down to an acetyl content of 32% or a partially hydrolyzedcellulose propionate having a hydroxyl content of approximately 7% asthe starting material for preparing the cellulose acylate sulfateproducts in accordance with our invention.

The sulfating agent, the neutral alkali metal salt of acyl sulfuricacid, is first prepared and is then incorporated in the acylating mass.For instance, to prepare the sodium salt of acetyl sulfuric acid 7 partsof 95% sulfuric acid are mixed with 25 parts of acetic anhydride, themixing being carried out at a temperature below 25 C. 5.7 parts ofsodium acetate are then added with continued cooling. The mixing iscontinued until the sodium acetate is dissolved. There is thus obtaineda clear solution of the sodium salt of acetyl sulfuric acid containingno excess sulfuric acid therein. To prepare the sulfating acylatingmixture there is then added the acid catalyst and the lower fatty acidanhydride and the diluent to be employed, whereupon the cellulosematerial is mixed therewith at a temperature Within the range of 60100F. until a test sample shows complete Water solubility. In the operationof the procedure in accordance with our invention, the sulfating agentcontains no free acyl sulfuric acid and a weak acid catalyst is used inpromoting the esterification procedure.

The following examples illustrate our invention:

Example 1 To 25 parts of acetic anhydride were added 7 parts of 95sulfuric acid, keeping the temperature of the solution below 25 C.during the addition. 5.7 parts of sodium acetate were then added, againcooling the mixture. After the last of the sodium-acetate had dissolved,10 parts of an 0.65 molar solution of sulfoacetic acid in 50:50 aceticacid: acetic anhydride were added.

This sulfating mixture was then added to a slurry of i 10 parts of woodpulp (which had been water activated and dewatered with acetic acid) in100 parts of acetic anhydride and 113 parts of acetic acid. Theresulting heterogeneous mixture was held at until a test sample showedcomplete water solubility. This particular reaction mixture andconditions required 45 minutes. The mass was suction filtered, Washedwith acetic acid, isopropyl alcohol and then with isopropyl alcoholcontaining enough ammonium hydroxide to neutralize any catalyst andacetic acid remaining. After another wash with isopropyl alcohol, theproduct was dried at 50 C. overnight. Analyses of the product were: pecent total sulfur, 8.7; percent apparent acetyl, 22.5; intrinsicviscosity 2.4.

Example 2 A sulfating mixture was prepared as described in Example 1with the exception of the Weak acid catalyst. In place of thesulfoacetic acid, 1.3 parts of phosphoric acid were added. This mixturewas then added to a slurry -F. with stirring Example 3 p 300 parts ofwood pulp having a moisture content of 7% were mixed with 200 parts ofacetic acid in a Werner- Pfleiderer mixer for 1 /2 hoursat 100 F. Themass was then cooled to 70 Rand a mixture of 100 parts of aceticanhydr-ide and 800'parts of acetic acid was added thereto.

There was independently prepared an acetylating-sulfa ting solutionby-the following steps: 200 parts of 95% sulfuric acid was slowly addedto 700' parts of acetic anhydride, the rate of addition being such thatthe temperature stayed below 25 C. There was then slowly added 159.5parts of sodium acetate-and the temperature was still maintained below25 C. 300 parts of 0.65 molar (0.65 mole per 1,000 partsof solvent)sulfoacetic acid were added. This esterifying liquid was added to themixer containing the cellulose and the reaction was run at 70*;F. untila watersoluble product was obtained. 200

parts of 75% acetic acid were then slowly added without 7 allowing thetemperature torise, followed by the addition of 1,000 parts of 'water.After 1 hour at 70 F. there was added 25 parts of sodium acetate and 100parts of 50% acetic acid following which by-adding 1,600-parts ofisopropyl alcohol to the-mixer. Theproduct was washed with isopropylalcohol and was found upon analysis to be water soluble sodium celluloseacetate sulfat'e having a sulfur content of 8%; and an acetyl content of21% we havs also'foun'd that sodium acidand a' lowerfatty acid anhydridemay bereacted to prepare the sodium salt of acyl sulfuric acid andliberate phosph'oricacid. The mixture of sodium salt of acyl sulfuricsedans phosphoric'acid thus prepared mixed with lower fat-tyacid andlower fatty acid anhydride, such as aceticjpr'opionic'or butyric acidand anhydride, may be reacted with cellulose to produce celluloseacylate-sulfates.

Various procedures may be employed in carrying out this feature of ourinvention. Thus, acyhsulfuric acid may be prepared by adding sulfuricacid to a lower fatty acid anhydride while keeping the temperature below25: C.-and sodium' phosphate may be added ther eto. ternatively,"sulfuric' acid may be added to a mixture of lower fatty acid anhydride,lower fattyacid, and sodium phosphate. Although monobasic or dibasicsodium phosphate'may be employed, we prefer to utilize trisodiumphosphate. It is desirable that the-sodium phosphate be anhydrous toavoid destroying lower fattyacid 'anhydride.

Examples-6 and 7 which of cellulose acylate sulfates inaccordance withour invention. Examples 4 and 5 illustrate the preparation of sodiumacyl sulfuric acid with liberation of phosphoric acid in accordance withour invention.

Example 4 andphosphoric acid has utility for esterifying cellulose.

Example} Acyl sulfuric acid was prepared by adding seven parts of 95percent sulfuric acid to20 parts of acetic anhydride while keeping thetemperature below 25 C. I 3.8 parts of anhydrous trisodium phosphate wasadded to the solution the product was precipitated:

follow illustrate the preparing phosphate, sulfuric and stirred untilthe sodium salt of acyl sulfuric acid formed therein was dissolved.

The following examples demonstrate the sulfation and acylation ofcellulose with acyl sulfuric acid and phosphoric acid as catalyst,utilizing mixtures like those prepared in Examples 1 and 2.

Example 6 The solution prepared in Example 5 was addedto aslurry'consisting of 10 parts of pulp, 138 parts of acetic acid andpar-ts of acetic anhydride (l3 parts ofthe acetic acid was on the pulpas a result of dewatering the water-activated pulp with acetic acid).The mixture was stirred at roomtemperature for 3.5 hours with nocooling.

The productwas collected in a filter, washed several times withisopropanol, then with a solution-of isopropanol 22.7 percent acetyl. Itwas completelywa-ter soluble.

Theesterification is conveniently carried out at a temperature withinthe range of 15-38 C. No -neutral. sodium sulfate was formedandsubstantial.esterificatiom of thecellulose was obtained.

Example 7 with 31.4 grams of aceticfacid at.. 43.- hour and then cooled.A reaction {6 hours) and 50% The product was isolated by adding dried at50 C. and contained 5-10%';of. combined sulfur and more than 20%.acetyl.

Ordinarily it is ,desirableto employ cellulose. asthe a startingmaterial but if desired, one may. employ a cel-. lulose ether such asethyl cellulose having esterifiableghw; droxyl groups or a partiallyhydrolyzed celluloseester such as cellulose acetatewhich hasbeen-hydrolyzeddown to an acetyl content of 3 2 percent orcellulosepropionate having a hydroxyl contentof approximately7 percentas the starting material. for preparing cellulose, acylate;

sulfate in accordance with our] invention.

The invention has been describedin' detail with partic-v ular referenceto preferred embodimentsthereof butit will be understood/that variationsand modifications can beefiected within the spirit and scope-70f theinvention as described hereinabove and as definedin the appended claims.

The compounds of this invention. are water solubleand may be made intofilms which are useful as water. soluble wrappings.

We claim:

1. A method .of preparing cellulose acylate sulfates, which comprisesreacting upon a cellulose material containing free and esterifiablehydroxyl groups with ,a mixture free of, acyl sulfuric acid of lowerfatty acid anhydride, an alkali metal salt of acyl sulfuric acid .asthesulfating, agent and as the catalyst, an acid which is weaker than thefirst hydrogen and stronger-than the second hydrogen, of sulfuric acidin acetic acid, at a temperature of 60-100 F. until a water solubleproduct is obtained.

2. A method of preparing a cellulose acylate sulfate which comprisesreacting upon cellulose with an esterification mixture free of acylsulfuric acid comprising a lower. fatty acid anhydride, an alkali metalsaltof acyl-sulfuric. acid and as the esteriiication catalyst, an acidweaker than the first hydrogen and stronger than the second hydrogen ofsulfuric acid in acetic acid, at a temperature containing sufficientammonium hydroxide to neu-l tralize any free acid, and again withisopropanoh The: dried product analyzed as follows: 8.1% percent-sulfurof 60-100" F. for a time sufiicient to impart complete water solubilityto the product.

3. A method of preparing cellulose acetate sulfate which comprisesesterifying cellulose With an esterification bath comprising a mixturefree of acyl sulfuric acid of acetic anhydride, an alkali metal salt ofacetyl sulfuric acid and as the catalyst, an acid weaker than the firsthydrogen and stronger than the second hydrogen of sulfuric acid inacetic acid, at a temperature of 60100 F. until the product iscompletely water soluble.

4. A method of preparing a cellulose acylate sulfate which comprisesreacting upon cellulose with an esterification mixture free of acylsulfuric acid comprising lower fatty acid anhydride, an alkali metalsalt of an acyl sulfuric acid and as the catalyst, sulfoacetic acid at60- 100 F. until a product having complete water solubility is obtained.

5. A method of preparing a cellulose acetate sulfate which comprisesesterifying cellulose with an esterifying bath free of acyl sulfuricacid comprising acetic anhydride, an alkali metal salt of acetylsulfuric acid and as the catalyst sulfoacetic acid at 60-100 F. until aproduct having complete water solubility is obtained.

6. A method of preparing a cellulose acetate sulfate which comprisesesterifying cellulose with an esterifying bath free of acyl sulfuricacid comprising acetic anhydride, an alkali metal salt of acetylsulfuric acid and as the catalyst phosphoric acid at (SO-100 F. until aproduct having complete water solubility is obtained.

7. A method of preparing a cellulose acetate sulfate which comprisesesterifying cellulose with an esterifying bath free of acyl sulfuricacid comprising acetic anhydride, an alkali metal salt of acetylsulfuric acid and as the catalyst methane sulfonic acid at 60-100 F.until a product having complete water solubility is obtained.

8. In the method of sulfating and acylating cellulose materialcontaining free and esteriifiable hydroxyl groups with an esterificationbath containing a lower fatty acid anhydride and a mixture of an alkalimetal salt of acyl sulfuric acid as the sulfating agent and phosphoricacid as the catalyst, the step which comprises preparing the mixture ofalkali metal salt of acyl sulfuric acid and phosphoric acid by combiningalkali metal phosphate and acyl sulfuric acid.

9. In the method of sulfating and acylating cellulose materialcontaining free and esterifiable hydroxyl groups with an esterificationbath containing a lower fatty acid anhydride and a mixture of an alkalimetal salt of acyl sulfuric acid as the sulfating agent and phosphoricacid as the catalyst, the step which comprises preparing the mixture ofalkali metal salt of acyl sulfuric acid and phosphoric acid by combininglower fatty acid anhydride and alkali metal phosphate and addingsulfuric acid thereto.

10. The method of sulfating and acylating cellulose which comprisesadding alkali metal phosphate to acyl sulfuric acid, and reacting theresulting mixture, together with lower fatty acid anhydride, withhydroxyl containing cellulose material.

11. The method of sulfating and acylating cellulose which comprisesmixing a lower fatty acid anhydride and sodium phosphate, addingsulfuric acid thereto, and reacting the resulting mixture, together withlower fatty acid anhydride, with a cellulose compound containing freeand esterifiable hydroxyl groups.

12. The method of preparing cellulose acetate-sulfate which comprisesadding anhydrous trisodium phosphate to acetyl sulfuric acid andreacting the resulting mixture, together with acetic acid and aceticanhydride, with cellulose.

13. The method of preparing cellulose acetate sulfate which comprisesmixing acetic anhydride and anhydrous trisodium phosphate, addingsulfuric acid thereto, and reacting the resulting mixture, together withacetic acid and acetic anhydride, with cellulose.

Sindl Jan. 10, 1939 Dowdall Feb. 10, 1953

1. A METHOD OF PREPARING CELLULOSE ACYLATE SULFATES WHICH COMPRISESREACTING UPON A CELLUSOSE MATERIAL CONTAINING FREE AND ESTERIFIABLEHYDROXYL GROUPS WITH A MIXTURE FREE OF ACYL SULFURIC ACID OF LOWER FATTYACID ANHYDRIDE, AN ALKALI METAL SALT OF ACYL SULFURIC ACID AS THESULFATING AGENT AND AS THE CATALYST, AN ACID WHICH IS WEAKER THAN THEFIRST HYDROGEN AND STRONGER THAN THE SECOND HYDROGEN OF SULFURIC ACID INACETIC ACID, AT A TEMPERATURE OF 60-100*F. UNTIL A WATER SOLUBLE PRODUCTIS OBTAINED.